1. Display Devices
• The most commonly used display device is a video monitor.
• The operation of most video monitors based on CRT
(Cathode Ray Tube).
• The following display devices are used:
• Refresh Cathode Ray Tube
• Random Scan and Raster Scan
• Color CRT Monitors
• Direct View Storage Tubes
• Flat Panel Display
2. Cathode Ray Tube (CRT)
• CRT stands for Cathode Ray Tube.
• CRT is a technology used in traditional computer monitors and
televisions.
• The image on CRT display is created by firing electrons from the
back of the tube of phosphorus located towards the front of the
screen.
• Once the electron heats the phosphorus, they light up, and they are
projected on a screen. The color you view on the screen is
produced by a blend of red, blue and green light.
4. Components of CRT
• Main Components of CRT are:
• Electron Gun: Electron gun consisting of a series of elements,
primarily a heating filament (heater) and a cathode. The electron
gun creates a source of electrons which are focused into a narrow
beam directed at the face of the CRT.
• Control Electrode: It is used to turn the electron beam on and
off.
• Focusing system: It is used to create a clear picture by focusing
the electrons into a narrow beam.
5. Components of CRT
• Deflection Yoke: It is used to control the direction of the electron
beam. It creates an electric or magnetic field which will bend the
electron beam as it passes through the area.
• Phosphorus-coated screen: The inside front surface of every
CRT is coated with phosphors.
• Phosphors glow when a high-energy electron beam hits them.
Phosphorescence is the term used to characterize the light given
off by a phosphor after it has been exposed to an electron beam.
6. Random Scan and Raster Scan Display
• Random Scan System uses an electron beam which operates like a
pencil to create a line image on the CRT screen.
• The picture is constructed out of a sequence of straight-line
segments. Each line segment is drawn on the screen by directing
the beam to move from one point on the screen to the next, where
its x & y coordinates define each point.
• After drawing the picture. The system cycles back to the first line
and design all the lines of the image 30 to 60 time each second.
8. Random Scan
• Random-scan monitors are also known as vector displays or
stroke-writing displays.
• Advantages:
• A CRT has the electron beam directed only to the parts of the
screen where an image is to be drawn.
• Produce smooth line drawings.
• High Resolution
9. Raster Scan Display
• A Raster Scan Display is based on intensity control of pixels in the
form of a rectangular box called Raster on the screen.
• Information of on and off pixels is stored in refresh buffer or Frame
buffer. Televisions in our house are based on Raster Scan Method.
• The raster scan system can store information of each pixel position,
so it is suitable for realistic display of objects. Raster Scan provides
a refresh rate of 60 to 80 frames per second.
10. Raster Scan Display
• Frame Buffer is also known as Raster or bit map.
• In Frame Buffer the positions are called picture elements or pixels.
• Beam refreshing is of two types. First is horizontal retracing and
second is vertical retracing. When the beam starts from the top left
corner and reaches the bottom right scale, it will again return to the
top left side called at vertical retrace. Then it will again more
horizontally from top to bottom call as horizontal retracing
12. Differentiate between Random and Raster Scan
Display
Random Scan Raster Scan
1. It has high Resolution 1. Its resolution is low.
2. It is more expensive 2. It is less expensive
3. Any modification if needed is
easy
3.Modification is tough
4. Solid pattern is tough to fill 4.Solid pattern is easy to fill
5. Refresh rate depends or
resolution
5. Refresh rate does not
depend on the picture.
6. Only screen with view on an
area is displayed.
6. Whole screen is scanned.
7. Beam Penetration
technology come under it.
7. Shadow mark technology
came under this.
8. It does not use interlacing
method.
8. It uses interlacing
9. It is restricted to line drawing
applications
9. It is suitable for realistic
display.
13. Color CRT Monitors
• The CRT Monitor display by using a combination of phosphors. The
phosphors are different colors. There are two popular approaches for
producing color displays with a CRT are:
• Beam Penetration Method
• Shadow-Mask Method
• Beam Penetration Method:
• The Beam-Penetration method has been used with random-scan monitors.
In this method, the CRT screen is coated with two layers of phosphor, red
and green and the displayed color depends on how far the electron beam
penetrates the phosphor layers.
14. Beam Penetration Method
• This method produces four colors only, red, green, orange and
yellow. A beam of slow electrons excites the outer red layer only;
hence screen shows red color only. A beam of high-speed electrons
excites the inner green layer. Thus screen shows a green color.
15. Shadow-Mask Method
• Shadow Mask Method is commonly used in Raster-Scan System
because they produce a much wider range of colors than the beam-
penetration method.
• It is used in the majority of color TV sets and monitors
• A shadow mask CRT has 3 phosphor color dots at each pixel
position.
• One phosphor dot emits: red light
• Another emits: green light
• Third emits: blue light
• This type of CRT has 3 electron guns, one for each color dot and a
shadow mask grid just behind the phosphor coated screen.
17. Shadow-Mask Method
• The deflection system of the CRT operates on all 3 electron beams
simultaneously; the 3 electron beams are deflected and focused as a
group onto the shadow mask, which contains a sequence of holes
aligned with the phosphor- dot patterns.
18. Direct View Storage Tubes
• DVST terminals also use the random scan approach to generate the
image on the CRT screen.
• The term "storage tube" refers to the ability of the screen to retain
the image which has been projected against it, thus avoiding the
need to rewrite the image constantly.
• Primary guns: It is used to store the picture pattern.
• Flood gun or Secondary gun: It is used to maintain picture
display.
20. Flat Panel Display
class of video devices that have:
• Reduced volume
• Reduced weight
• Reduced power requirement
in compared to a CRT.
21. Flat Panel Display
– The important feature of FPD is that they are thinner than
CRTs.
– There are two types of Flat panel display: Emissive display
and Non-emissive display.
– Classification of Flat panel Displays : {Plasma and LCD
Displays}
22. Flat Panel Display
• Emissive Display:
– They convert electrical energy into light energy. Plasma
panels, thin-film displays, and light emitting diodes are
example of emissive displays.
• Non-emissive Display:
– They use optical effect to convert sunlight or light from some
other source into graphics patterns. Liquid crystal display is an
example of non-emissive display.
23. Uses of Flat Panel Displays
• Small Tv monitors
• Calculators
• Pocket video Games
• Advertisement Boars in elevators
